Timing device



seprn 14, 1943.

G. 1. HOLMES TIMIM `DEVICE Filed July'8. 1942 INVENTOI.

I. HOL/V55 f BY dfb/K M roamed sopa 14, 1943 UNITED STATES 2,329,614' 'rrMING DEVICE Gillord 1. Holmes, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., a

corporation lof Delaware Appiioanon July s,1s4 2,sern1 No. 450,159

6 Claims.

The present invention is concerned with a timing device and more particularly with' one employing a thermally operated timing element.

A broad object ofthe invention is to providea thermal timing device in which a high degree of heat insulation is obtained so as to provide relatively long cooling periods as compared with the heating periods.

A still further object of the invention is to provide such a timing device in which means is provided for predetermining the rate of cooling.

A still further object of the invention is to provide such a timing device whichthe timed device is a switch.

These and other objects which will be apparent from the accompanying specification, claims, and drawing, are accomplished broadly by providing a double walled receptacle in which the walls are provided with a reflecting coating and in which the space between the walls is evacuated so as to decrease the heat conductivity therebetween. The various timingl elements including a thermosensitive element and a heater are mounted through an opening in said receptacle which is sealed by a plug of predetermined heat conductivity. This plug serves to support the timing element and provide means for connecting them with external conductors.

The drawing shows a sectional view of my new timing device in the form of a time switch. In the drawing, the time switch acts as a controlling element in a stoker control system which is shown schematically for convenience of illustration.

Referring to the drawing for a more detailed understanding ofv the invention, my improved timing device is generally indicated by the reference numeral Ill. This timing device comprises generally a double walled receptacle II and a Aclosure plug I2 supporting a contact carrying strip I3, a bimetallic strip M and a heater I5.' These various elements will now beldescrib'ed in more detail. y

The double walled receptacle II comprises two spaced walls I1 and`I8. 'I he walls I'i and Il are uniformly spaced throughout, being connected together at their ends by an annular portion I! so as to form a sealed chamber. 'I'he innermost surface of outer wall -I'I is provided with a silver coating 2l. YA similar silver coating 2l is provided on theouter'surface ofthe inner wall I8. These silver coatings 2l and 2| act as vreiiectin'g coatings to reflect back heat either entering or leaving th'ei'receptacle.- The space between' the walls I1 and IB-is evacuated so as to decrease the heat conductivity through this space. The

. thatthespaceis sealed, prevents the silver coat- 5 ings 20 and 2l from becoming tarnished. v

It will be noted that the receptacle I I is in the form of an elongated open ended chamber. The plug I2 is sealed in theopen end of this chamber and` acts as a closure. The plug vI2 is preferably of material of predetermined heat conductivity so that by selecting a plug of the proper material, any desired rate of cooling of the timer may be obtained.

The c ontact carrying strip, the bimetallic element Il and the heater I5 are supported by the plug l2 longitudinally of the receptacle. Associated with the` contact carrying strip I2 and the bimetallic lelement I4 are contacts 25 and 25. As indicated by the legend adjacent the lower end of the bimetallic element Il the bimetallic element I I is adapted to'warp to the right upon being heated. Such warping movement will cause separation of contacts and 26 .The heater element I5 extends longitudinally 25 of the bimetallic element for substantially the full length thereof. At its lower end it is electrically connected by a conductive member 21 to .contact 26 through 'bimetallie element I4. At its upper end it is secured to a terminal strip 28 30 extending through the plug I2.

When the heater I5 is energized. the bimetallicA element Il is heated so that it warps to the right causing separation of contacts 25 and 26. This not only breaks a -controlled circuit in a manner to be described later, but it Aalso interrupts the circuit to heater I5. 'The contacts 25 and 26 are not reengaged until the bimetallic element I4 has cooled to the point where such reengageme'nt is o possible. Because of the extremely small heat conductivity through the evacuated `space between th'e two walls and due to the tendency of the silvered surfaces 2l and 2l to reiiect back anygheat tending to leave, the majority of the heat leaving thel receptacle is that conducted by plug I2. Obviously, by forming. the plug of material having a desired rate of heat conductivity,

a cooling period of any desired length can be obtained. 5o The timing switch is shown in the drawing as an nement of o. Stoker oontroi system in order to better illustrate the operation of the switch. In a conventional type of stoker control system, itis desirable to provide some means for periodo ioaliy oonsing operation or the Stoker when the evacuation of this space, together with the factv lmeral 3i. Thisstoker serves to feed coal to a furnace 32 and comprises means for supplying the proper draft to the fuel bed of the furnace. A relay 34 directly controls the operation of the stoker motor 3G. VThis relay comprises a relay coil 35, a relay switch blade 36, and a switch contact 3l. The relay switch blade 36 is normally biased out of engagement with contact 37 by gravity or any other suitable biasing means. Upon the relay coil 35 being energized, the switch Jblade 36is moved into engagement with Contact A room thermostat 3511s Vemployedto.control the'operation of the stoker in conjunction with the time switch i6. This thermostat comprises a bimetallic element to whicljigiswsecured e contact arnilg-'hercontfat/arm do is movable m o and out of engagement with a iixed contact di. The bime'tallic element is so arranged that upon a drop in the temperature aiecting the bimetallic element, it moves-the contact arm dt On the other.

to the right towards contact l'i. hand, when the temperature rises the contact arm 40 is moved to the left away :from contact 5I. This is indicated in the drawing by the legends C and HP v Power for operation of the relay 34 is supplied vby a step-down transformer dii. This transformer comprises a line voltage primary winding 45 and a low voltage secondary winding 46. The line voltage primary winding 45 is connected by conductorsdl and 58 to line Wires 49 and 55 leading to any suitable source of power (not shown).

Operation `The various elements are shown in the position they occupy when the room thermostat' is satised. Under these conditions, the stoker is beingoperated under the control of the time switch IIJ. It is to be noted that with the elements in the position shown, an energizing circuit is established to relay winding 35 of relay 34 as follows: from the upper terminal of through conductors 5I and 52,'contact strip I3,

contacts 25 and 26, conductive element 2l, heater I5, terminal strip 28, conductor 53, relay Wind- 49 through conductor 55, contact 31, switch blade 36, conductor 56, stoker motor 30, and conductor 51 to the other line Wire 50. Because of the closure of the circuit, the stoker motor 30 is relay coil 35 is interruptedY so as to cause deenergization of relay 34. Such deenergization results inV interruption of the circuit traced tov stoker motor 3U so that the stoker is placed out ofI operation. Separation of contacts and 26 also causes the circuit throughheating element I5 to be interrupted so that bimetallic element I4 is no longer being heated .by this heater and hence begins to cool. This cooling is relatively slow, however, due to the fact that the -space within the receptacle has also been heated to a certain degree by the heater I5 and the heat passes out of the receptacle at an extremely slow rate, largelydetermined by the heat conductivity of the plug l2. As aresult, a considerable cooling time elapses before contacts 25 and 25 reengage. In one typical case, the timing device is so constructed as to provide a two minute period during which the contacts 25 and `26 are closed and a thirty minute cooling period during which contacts 25 and 26 areopened.

If during this cooling period the thermostat 38 does not call for heat, contacts-25 and 25 will f Ramses/bs to reestablish the energizing circuit.l rtoireiay coil V previously traced. This in turn cause operation of the stoker for another secondary Winding 46 Q Just traced will he ing 3,5, and conductor 54 to the lower terminal opened so as to cause fuel and air to be supplied i to the furnace 32.

. It will be 'noted that the circuit traced torelay winding 35 included the electric heater I5. Because of this, the electric heater I5 will operate to heat the bimetallic element I4 so that this bimetallic'eleinent will tend to warp to the right. After a predetermined heating period has elapsed, contacts 25 and 26 will be separated. When they do separate, theV circuit traced to the Obviously, when the Thus,.so long as the heating period. It will be seen that, disregardingthe action of thermostat 38,' the time switch ii serves to periodically operate the stolzer 35 for brief periods of time.

When the thermostat 3B calls for heat, that is, vwhen the temperature adjacent bimetallic element 39 drops suiiiciently to cause engagemerit of contact arm d@ with contact di, the :following circuit is established to relay coil 35: from the upper terminal -of secondary winding 35, through conductors 5I and tfoontact l i, contact arm 4G, bimetallic element'i, conductor 6i, bimetallic element i4, conductive element 2l, heater I5, terminal strip 28, conductor 53, relay coil 35, and conductor 54 to the lower terminal of secondary winding 45. This, in turn, causes relay 34 to `move to its energized position so as to cause closure of the energizing circuit to the stoker motor 30, previously traced. lt will be noted that the circuit just traced is independent of contacts 25 and 23 so that the stoker will continue to operate so long as thermostat contact blade 4B is in engagement with contact 4i. When the temperature inthe space due to operation of the stoker 3| has rrisen sumciently to cause operation of contacts 4E? and 4i, the circuit interrupted so as to cause termination of the operation of the stoker.,

It would be undesirable for the timer lll tocause operation of the stoker immediately after a prolonged operation of the stoker under the control of the thermostat 3B. With the System shown in the drawing, this is avoided; It is to be noted thatA the thermostat circuit to relay coil 35 extends' through t1the heating element I5.

ermostat 38 is callinV gv fo heat the heaterI5 is being energized. The heat er I5 is thus eiective normally to cause separation of contacts 25 and 26. 'I'hese contacts can-VM not reclose, moreove until the heat produced by the energization of heater I5 has been dissipated.

thermostat has been calling for heat for a substantialperiod of time, the coolmg period will necessarily be somewhat greater than with a normal operation of the timer Il. This insures that the timer I0 will not cause the stoker motor 30 to be placed into operation as quickly as it would if it had been previously operated for' merely a shortperlod under thecon- 3. A thermal timing device comprising a double wall receptacle having an opening through the two walls thereof, the space between the walls of said receptacle being evacuated to decrease the heat conductivity thereof, a thermosensitlve element, an element actuated thereby, a heater for heating said thermosensitive not only acts as a support for the timing elements but also as a means' of determining the timing ofthe timing device. A further function of the plug I2 is that of providing means for connecting the timing elements to external conductors.

It will be noted from the preceding description that contact carrying blade I3 is connected to conductor 52, bimetallic element I4 to conductor 6I, and heater I5 to conductor 53 by means of terminal strip 28. Thus, the plug I2 provides means by which thewlements I3, I4 and I5 10- cated entirely withinthe receptacle II are'connected to other circuit elements. Y

The silver reflecting coatings and 2l, as previously noted, not only serve to prevent the heat from leaving the receptacle but also serve to retard the entrance' of heat into the receptacle. Because of this, the timing period is relatively unaffected by changes in ambient temperature. This freedom from the effects of changes in the ambient temperature canv be further increased by adjusting the timer so that the switch contacts and 26 are closed at a temperature considerably abbve ambient tem.- perature. If this is done, the temperature within the receptacle will always be substantially above the ambient temperature so as to be relatively unaffected by ambient temperature.

It will be seen that I have provided an extremely simple thermal timing device particularly adaptable for use as a timing switch in a stoker control system. While it is particularly suitable for this application, it obviously can be employed in many other applications where it isl desirable to have relatively short heating periods as compared with the cooling periods.

element, and a separate plug -closing said opening and supporting said thermosensitive element, said actuated element, and said heater within said receptacle.

, 4. A thermal timing device comprising a `double wall receptacle having an opening through two walls thereof, the outer surface of the inner wall and in the inner surface of the outer wall of said receptacle being provided with a reflecting coating andthe space between said walls being evacuated to decrease the heat conductivity thereof, a thermosensitive element, an

` double wall receptacle having element actuated thereby, a heater for heating said thermosensitive element, and a separate plug of material of predetermined heat conductivity closing said opening and supporting said thermosensitive element, said actuated element, and said heater within said receptacle.

5. A thermal timing device comprising a l inner and outerspaced cylindrical walls both closed at one end and integrally joined together at their opposite open ends so as to provide a sealed chamber between said wa1ls,said chamber being evacuated to decrease the heat conductivity thereof, a thermosensitive element, an element actuated thereby, a heater for heating said thermosensitive element, and a separate flanged plug of material of predetermined heat conductivity projecting into and closing the open end of said inner wall with the flange thereof overlying the joint between said inner and outer walls, said plug closing said opening and supporting said thermosensitive elements, said actuated element, and said heater within said receptacle. K

6. A thermal time switch comprising a double wall receptacle having inner and outer spaced cylindrical walls both closed at one end and integrally joined together at their op- In general, while I have shown a specific embodiment of the invention, it is to be understood that this is for purposes of illustrationl and that the invention is to be limited only by the scope of the appended claims.

I claim as my invention:

ll. A thermal time switch comprising a thermally operated switch, a heater therefor, a double Walled receptacle completely enclosing said switch and heater except for an opening in said'receptacle, and a, separate plug of material of predetermined heat conductivity closing the opening in said receptacle.

2. A thermal time switch comprising a thermally operated switch, Aa heater therefor, a `double walled receptacle completely enclosing said switch and heater except for an opening in said receptacle, and a separate plug of material of predetermined heat conductivity closing the opening in said receptacle; said switch and posite ends so as to provide a sealed chamber between said walls, said chamber being evacuated to decreasethe heat conductivity thereof, a thermosensitive element, a' first contact position thereby, a second contact,a contact'carrying strip thereforva heater for heating said thermosensitive element to cause separation of said contacts, said thermosensitive element being so disposed with respect to said contacts carrying strip that said contacts are re-engaged when the temperature of said thermosensitive element is still substantially above ambient temperature, and a separate iianged plug of material or predetermined heat conductivity projecting into and closing the open end of saId inner wall with the flange lthereof overlying the joint between said inner and outer walls, said plug closing said lopening and supporting vsaid thermosensitive heater being secured to said plugv and supported thereby.

element, said contact carrying strip, and said heater with said receptable.

. Grr'r'onn LHoLims. 

